The Atom

In the nucleus (nucleons)

Proton- (+) charged particle
Neutron- no charge

Outside the nucleus

Electron- (-) charged particle
has almost no mass

Nucleons

• Are particles occupying the nucleus
• Consist of + charged protons and neutral

neutrons

• Have almost 2000 times the mass of

electrons

• Where can you find the number of protons?
• It’s the atomic number (found on the periodic

table)

Nuclear Notation

Atomic number = no. of protons

Atomic mass = protons + neutrons

Atomic number is the same as the number of electrons
in an uncharged atom

5
B

10.811

Atomic Number

Atomic Mass

1a. How many protons?
1b. How many neutrons?
1c. How many nucleons?

You may see atomic number written many ways. The smaller
number is the atomic number and the larger is the atomic
mass

Question 1

• has 13 protons and 14 neutrons for a

total of 27 nucleons

• has 13 protons and 15 neutrons for a

total of 28 nucleons

• The identity of an element depends

on the number of protons

28

Isotopes:

• Atoms of the same element with different

numbers of neutrons (different masses)

Most common
stable isotope
of carbon

Unstable
radioactive isotope
of carbon